Field of the Invention
This invention relates to elastic hard fibers composed mainly of polyisobutylene oxide and which have an extremely high work recovery ratio, and to elastic hard fibers which have in combination a highly elastic behavior and a high work recovery ratio, and to a process for manufacturing such elastic hard fibers.
Most fibers have inherent elastic properties and they exhibit an elastic recovery property such that when they are deformed by an externally applied stress, for example, when they are elongated by a tensile stress, and the stress is then removed, they tend to return to their original configuration. Among the various properties of fibers, one of the properties of high practical value in connection with recovery from shrinkage, creasing or wrinkles, is that the fibers have a high elastic behavior and a high work recovery ratio when applied stress is removed. It is reported that among the commercially available fibers, nylon fibers possess the most excellent elastic recovery characteristics. It is reported that, for example, 210 denier nylon yarns exhibit an initial recovery ratio of 78% and an overall recovery ratio of 95% from 30 - 50% extension (see "Synthetic Fibers," pages 157 and 783 written by Sakurada, Sofue, and Kushii and published by Asakura Shoten). The initial recovery ratio means the elastic recovery ratio immediately after the fibers are taken up and the overall recovery ratio means the elastic recovery ratio after when the fiber is maintained at a predetermined length for a predetermined period and is then relaxed and allowed to stand still for a sufficiently long time (e.g. 24 hrs.).
However, when most fibers are stretched or elongated, a considerable plastic deformation occurs and they are unable to return completely to their original length. Further, when extension and relaxation are repeated, strain is left in the fibers and they are likely to be stretched considerably or to be broken.
Elastomer fibers are mentioned as an example of fibers having a high elastic recovery ratio. Typical examples of such fibers are Spandex fibers. According to the regulations of the United States Tariff Commission, it is specified that Spandex fibers are those in which "chains containing urethane linkages occupy at least 80% of the chemical structure constituting the fibers". In practice, these fibers exhibit a considerable elastic recovery ratio after 500 - 700% extension. A typical process for the manufacture of such Spandex fibers comprises synthesizing a diisocyanate and a cyclic ether, respectively, polymerizing the cyclic ether, polycondensing both the terminal groups of the polymerized cyclic ether with excess diisocyanate groups to form a prepolymer, and spinning it into a coagulation bath by the wet or dry method.
Thus, this process comprises a number of steps and the manufacturing cost of such fibers is very high. Further, these fibers have the defects that yellowing thereof readily occurs and body odor is likely to become present in the fibers. Accordingly, development of elastic fibers having a high elastic recovery ratio which can be manufactured at a low cost by a simple spinning method has heretofore been greatly desired in the art.
Recently, fibers of high elastic characteristics, called "elastic hard fibers", have been developed. For example, Japanese Patent Publication No. 9810/66 discloses a process for the manufacture of polypivalolactone fibers.
However, commercial utilization of polypivalolactone fibers has not succeeded because of the complicated procedures required for the synthesis of the monomers and because of the inherent instability of the lactone units against heat, acids, alkalis and the like.
In "Journal of Macromolecular Science, B5 (4), p. 721 (1971)", R. G. Quynn and H. Brody describe elastic hard fibers made of polypropylene, poly-3-methyl-butene-1 and polyoxymethylene. They state that although the mechanism of the highly elastic behaviors of these fibers has not sufficiently been elucidated as yet, the high elasticity of these fibers is deemed not to depend on the classical theory of rubber elasticity or the change in entropy; rather it is considered to be due to accumulated crystalline lamellas.
The "hardness" of elastic fibers referred to herein means a hard elasticity owing to the semimicroscopic states of the crystalline and amorphous portions of the fibers and it is not caused by a simple change in entropy such as is the case in the conventional elastic fibers. Said "hard elasticity" can be clearly distinguished from "soft hardness" in the conventional elastic fibers. The fundamental difference is apparent from the stress-strain curves shown in FIG. 1.
More specifically, FIG. 1 shows a stress-strain curve I of a typical elastic hard fiber, i.e. poly-3-methylbutene-1 fiber (plotted based on values given by Quynn et al. in "Journal of Macromolecular Science," B5, p. 721 (1971) and a stress-strain curve II of a typical elastic soft fiber, i.e., a Spandex fiber. As is apparent from FIG. 1, under the same extension, in the elastic soft fiber II the stress is extremely low as compared with the case of the elastic hard fiber I. For instance, under 50% extension, in a typical elastic soft fiber, i.e., a Spandex fiber, the stress is 0.03-0.04 g/denier (25.degree. C) but an elastic hard fiber has a stress more than 10 times as high. (For example, as is seen in FIG. 2 which illustrates the stress-strain curve drawn continuously and repeatedly with respect to the elastic hard fiber of polyisobutylene oxide manufactured by the process of this invention, the elastic fiber of this invention has a stress of 0.7-1.5 g/denier under the same elongation.)
We noted that these elastic hard fibers have in common with each other the characteristic that they are highly crystalline, high molecular substances and they have small regular branches (polyoxymethylene has regular hydrogen bonds which are considered to exhibit the same function as the branches). We studied polyisobutylene oxide which is a highly crystalline, high molecular weight polymer, despite the presence therein of polyether branches, in relation to the inherent rubbery elasticity of polyethers such as polyethylene oxide, polypropylene oxide and polyepichlorohydrin. Thus, we carried out our research with a view to developing elastic characteristics and behaviors in polyisobutylene oxide, and as a result, we discovered the present invention.